US6325771B1 - Chest compression apparatus for cardiac arrest - Google Patents

Abstract

The invention is an apparatus for increasing intrathoracic pressure for resuscitating cardiac arrest patients. The apparatus comprises a flexible, substantially inelastic belt wrapped around the patient's chest and attached to a force converter. The force converter converts a downwardly directed force into a chestward resultant, which depresses the sternum, and two belt tightening resultants. The force converter comprises a pair of arm assemblies, each having a pair of spaced arms, which are pivotably mounted to a base. The base is positioned near the patient's sternum and the ends of the belt attach to one end of each arm assembly. The opposite, handle ends of the arm assemblies are depressed toward the chest causing tightening of the belt and compression of the chest cavity.

Description

The present application is a continuation of U. S. patent application Ser. No. 09/059,497, now U.S. Pat. No. 6,234,984 filed Apr. 13, 1998, which is a continuation of U. S. patent application Ser. No. 08/573,465, filed Dec. 15, 1995, and issued as U. S. Pat. No. 5,738,637 on Apr. 14, 1998.

TECHNICAL FIELD

This invention relates broadly to the field of medical devices and more specifically to an apparatus for increasing the blood flow by compressing the chest cavity of a person suffering from cardiac arrest.

BACKGROUND ART

During cardiac arrest, it is desirable to generate blood flow by external means in order to maintain brain and heart viability. Traditionally, the external means of generating blood flow has been manual cardiopulmonary resuscitation (CPR). Using CPR, the rescuer tilts the patient's head back, lifts the chin to clear and straighten the airway, and depresses the sternum 1½ to 2 inches 15 times (at a rate of 80 to 100 depressions per minute), after which the rescuer gives the patient 2 full breaths. This 15 depressions and 2 breaths is repeated cyclically.

Currently, the CPR research community believes that blood flow produced by external means can be explained by one, or a combination of two, theoretical mechanisms: the “cardiac pump” mechanism and the “thoracic pump” mechanism.

According to the cardiac pump mechanism, blood flow caused by external means is due to direct mechanical compression of the heart. During compression, blood is squeezed out of the heart chambers, and during release of the compression (relaxation) blood flows into the heart chambers. Backflow of the blood is prevented by the valving of the heart and vessels.

According to the thoracic pump mechanism, blood is pumped by external means as a result of the cyclical increase and decrease of intrathoracic pressure. During compression, the intrathoracic pressure rises, which causes blood to be forced out of the blood vessels and organs located in the thorax, and the blood flows into the peripheral tissues. During release, blood flows back into the thorax via the normal venous return. In this method, backflow is prevented by the valving of the veins.

Most researchers believe that both mechanisms are active to some degree. However, the methods presently in use, and the devices currently in use, for promoting blood flow by the application of an external force are directed toward only one of the two mechanisms. In order to maximize blood flow, a device which takes advantage of both mechanisms is needed.

A variety of devices have been developed to increase blood and/or air flow in the chest cavity of a cardiac arrest patient.

U.S. Pat. No. 2,071,215 to Petersen shows a piston and cylinder arrangement attached to two ends of a girdle which encircles a patient's chest. The expansion or compression of a fluid in the piston and cylinder combination tightens and loosens the girdle to ventilate the lungs. This device is large and heavy, and is dependent upon a compressed fluid for driving power.

U.S. Pat. No. 3,425,409 to Isaacson et al. discloses an apparatus for compressing the sternum by a downward force generated by a piston. A belt is placed around the chest in order to minimize bodily damage, and air is applied to the air passages of the patient.

U.S. Pat. No. 5,287,846 to Capjon et al. shows an upper frame that rests on a patient, whose back rests on a lower frame. Retractable straps extend from the upper frame and attach to the lower frame. A hydraulic cylinder in the upper frame presses downwardly on the chest.

Barkalow, in U.S. Pat. No. 3,461,860, discloses a device using a pneumatic plunger to mechanically compress the sternum a predetermined distance. A mechanical ventilator was added to this device in U.S. Pat. No. 4,326,507 to insure proper ventilation and increase the volume of the chest. This device was limited in its success due to complexity which requires trained personnel to use it.

A similar device was disclosed in U.S. Pat. No. 4,060,079 to Reinhold. This device is merely a similar portable unit.

Bloom, in U.S. Pat. No. 4,338,924, shows a sternum compression device using an air cylinder to depress the chest of the cardiac arrest patient. This device, like many others using a chest compression design, is large and heavy.

Newman et al., in U.S. Pat. No. 4,424,806, show a pneumatic vest for generating a rise in thoracic pressure. This vest uses the “thoracic pump” concept of exerting greater force over a larger area under the assumption that if more major organs could be compressed and released, greater blood flow would occur. By releasing the compression force, the chest would return to its normal size and draw blood back into the major organs. Positive blood flow would occur due to the one-way valves in the vascular network. The Newman device is not readily portable, in addition to having substantial complexity. In U.S. Pat. No. 4,928,674, Halperin et al. disclose a similar vest which is similarly not portable.

Lach et al., in U.S. Pat. No. 4,770,164, disclose a circumferential band and take-up reel used to generate a rise in thoracic pressure. Although either manually or mechanically driven, this apparatus requires the use of a backboard for guiding the band around the chest.

The use of bands or belts to generate a rise in intrathoracic compression for the purpose of assisting respiratory ailments is disclosed in U.S. Pat. No. 651,962 to Boghean. This device is for periodic loosening and tightening of the band around a patient's chest for treating respiratory disease by regulating periods of breathing as well as the size or depth of breath.

In U.S. Pat. No. 3,777,744, Fryfogle et al. disclose a breathing aid consisting of a belt and a handle which tightens the belt for expelling excessive residual air in the lungs.

Other devices known to the Applicants using circumferential bands for generating a compression force on the abdomen and lower chest to assist in compression of lungs for respiratory purposes include U.S. Pat. No. 2,899,955 to Huxley, U.S. Pat. No. 3,368,5861 to Glascock and U.S. Pat. No. 2,754,817 to Nemeth. Furthermore, the use of inflatable bladders positioned around either the chest or the abdomen have been disclosed in U.S. Pat. No. 3,481,327 to Drennen, U.S. Pat. No. 3,120,228 to Huxley, U.S. Pat. No. 3,042,024 to Mendelson, U.S. Pat. No. 2,853,998 to Emerson, U.S. Pat. No. 2,780,222 to Polzin, U.S. Pat. No. 2,071,215 to Petersen, U.S. Pat. No. 4,424,806 to Newman and U.S. Pat. No. 4,928,674 to Halperin.

U.S. Pat. No. 2,699,163 to Engström, shows a respirator device for ventilating a patient's lungs.

U.S. Pat. No. 5,295,481 to Geeham shows a chest compression device comprising a T-shaped mechanical chest compression apparatus with a suction cup. The central shaft attached to the cup may be compressed beyond the lips of the cup and bruise or otherwise injure the patient due to the concentration of force on the patient by the shaft tip.

U.S. Pat. Nos. 4,397,306 to Weisfeldt et al. and 1,399,034 to Taplin show large mechanical devices for compressing the chest of a cardiac arrest patient.

Szpur, in U.S. Pat. No. 5,407,418, discloses a power-driven, pulsating compressor apparatus for stimulating blood flow within vessels of a person's foot or hand. The device periodically applies a concentrated force against a localized region of the foot or hand.

In spite of the prior art, the need still exists for a device which effectively increases the flow of blood in the organs of a cardiac arrest patient. This device should be truly portable and useable by a person of average strength and skill.

BRIEF DISCLOSURE OF INVENTION

The invention is an apparatus for increasing the flow of blood in a patient, for example a person suffering cardiac arrest. The apparatus comprises a base contoured to seat near a central region of the patient's chest. Also included are a manual actuator and a substantially inelastic belt which is for wrapping around the patient's chest. The invention further comprises a force converter mounted to the base. The force converter is connected to the actuator and has belt connectors for connecting to opposite extremities of the belt. The force converter is for converting a force manually applied to the actuator and directed toward the chest into a chest compressing resultant. The chest compressing resultant is directed through the base toward the chest. The force manually applied to the actuator is converted, in addition to the chest compressing resultant, into belt tightening resultants applied to the belt connectors, and directed tangentially to the chest.

The invention contemplates the converter comprising first and second assemblies. The first assembly has a pair of spaced, parallel arms rigidly connected at handle ends by a first hand-grippable handle. The arms of the first assembly are further rigidly connected at opposite, belt ends by a first strut. The first assembly arms are pivotally mounted to the base at a first assembly fulcrum intermediate the handle and belt ends. The second assembly is substantially similar to the first assembly and both assemblies are pivotally mounted to the base, forming a scissors arrangement. A force applied to the handle ends pivots the scissoring assemblies, which form a pair of levers. The strut ends of the assemblies are levered toward one another, tightening the belt attached to the struts.

It is an objective of the present invention to provide an apparatus having a flexible belt which wraps around the chest of a cardiac arrest patient. The apparatus tightens the belt while depressing the chest, the combination of which raises the intrathoracic pressure, enhancing blood flow.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view in perspective illustrating an embodiment of the present invention in an operable position;

FIG. 2 is a side view in section illustrating the extreme positions of the arm assemblies of the embodiment of the present invention shown in FIG. 1;

FIG. 3 is a diagrammatic view illustrating a force diagram;

FIG. 4 is a diagrammatic view illustrating an alternative force converter;

FIG. 5 is a diagrammatic view illustrating an alternative force converter;

FIG. 6 is a diagrammatic view illustrating an alternative force converter;

FIG. 7 is a diagrammatic view illustrating an alternative force converter;

FIG. 8 is a diagrammatic view illustrating an alternative force converter;

FIG. 9 is a view in perspective illustrating an alternative embodiment of the present invention;

FIG. 10 is an end view in section illustrating a prime mover actuator as part of the present invention;

FIG. 11 is a view in perspective illustrating an alternative embodiment of the present invention;

FIG. 12 is a diagrammatic view illustrating an alternative embodiment of the present invention;

FIG. 13 is a view in perspective illustrating an embodiment of the present invention;

FIG. 14 is an enlarged view in perspective of an embodiment of the present invention;

FIG. 15 is a side view in section illustrating the extreme positions of the arm assemblies of the embodiment of the present invention shown in FIG. 13;

FIG. 16 is a side view in section illustrating a sole of the base; and

FIG. 17 is a side view in section illustrating another sole of the base.

In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

DETAILED DESCRIPTION

FIG. 1 shows theapparatus10, which is an embodiment of the invention, in its operable position on and around a patient'schest12. Thebase14 is a semi-rigid (preferably plastic) plate or block, preferably having a cushioned outer surface contoured to seat against the central region of the patient'schest12 near the sternum. The sole92 of thebase14 is seated against the upper surface of thechest12 and may have an adhesive pad500 (shown in FIG. 16) or a suction cup502 (shown in FIG. 17) to adhere to thechest12 so that pulling on thebase14 will cause thechest12 to be pulled for decompression.

The base14 contains aswitch70 and a pair oflights72. Additionally, the base14 contains a battery, a battery charge indicator and a sound generator (not visible in FIG. 1) which sound generator emits an audible, periodic signal. The visible and audible signals indicate the frequency to a rescuer of a compressive force he or she is to apply to theapparatus10. One or more of the audible or visible signals could also prompt the rescuer to apply ventilation. The base14 also contains a force sensor, such as a strain gauge, and anindicator74 which indicates the force exerted on thechest12 to warn the rescuer of potential injury due to excessive force. A limiter could be added to limit some of the force applied to the patient to a specified maximum.

Thefirst arm assembly16 is made up of a pair of spaced,parallel arms22 and24 which are made of high tensile strength, lightweight material such as plastic. Thesecond arm assembly18 has substantially similar spaced,parallel arms26 and28. A pair ofrods37 and38 rigidly fasten the spaced parallel arms of theassemblies16 and18, respectively. A pair of manual actuators, which are preferably two cylindrical, hand-grippable handles30 and32, are rotatably mounted between the spaced, parallel arms of the first andsecond arm assemblies16 and18, around therods37 and38, respectively. A pair of rod-like, preferably metal struts34 and36 (strut36 not visible in FIG. 1) rigidly mount to the ends of the spaced arms, opposite thehandles30 and32.

Therigid arm assemblies16 and18 pivot relative to one another about thepivot pin20, which is preferably a stainless steel bolt. Thepin20 extends longitudinally through thebase14 and extends out of each longitudinal end to pivotally attach to eacharm22,24,26 and28.

Thearm assemblies16 and18 are arranged in a scissor-like configuration. This configuration is designed to convert a small force into a larger force. This is done by the scissor-like configuration having a pair of levers with a common fulcrum, where the fulcrum is located a distance from the center of the levers. A large displacement of thehandles30 and32 causes a relatively small displacement of thestruts34 and36. In elementary physics, it is understood that work equals force times distance and the force applied to cause a displacement at one end of a lever should equal the product of force and displacement at the opposite end of the lever. Conservation of work gives

F_sD_s=F_hD_h  Equation 1

where the subscript s indicates the force or displacement at thestruts34 and36 and the subscript h indicates the force or displacement at thehandles30 and32. Solving Equation 1 for the force at thestruts34 and36 obtains$\begin{array}{cc}{F}_s=\frac{F_hD_h}{D_s}.& \mathrm{Equation}2\end{array}$

The displacement at thestruts34 and36 (D_sin Equation 2) will always be smaller than the displacement at the handle (D_hin Equation 2). By separating the displacement part of Equation 2 in parenthesis, the following is obtained:$\begin{array}{cc}{F}_s=F_h\left(\frac{D_h}{D_s}\right).& \mathrm{Equation}3\end{array}$

Since the displacement at the struts is smaller than the displacement at the handles, the displacement portion of Equation 3 will be a number greater than 1 which, when multiplied by the force at the handles, will obtain a force at the struts which is greater than the force at the handles. It is this greater force at thestruts34 and36, effected by the force applied to the handles, which is used to artificially induce or enhance blood flow in a patient.

The pivoting motion of thearm assemblies16 and18 is a simple and reliable action which virtually any person can effectuate. Doing so requires a small force, and creates a larger force that is to be applied to a patient'schest12. The force at thestruts34 and36 could not be generated by an average person for the time period required to treat a cardiac arrest patient, without the help of a mechanical device.

Two stainlesssteel stroke limiters52 and54 are pivotally mounted to thearms22 and24 and slidingly attach to thearms26 and28. Thelimiters52 and54 serve the purpose of limiting the relative pivoting displacement of theassemblies16 and18 by mechanically restricting their movement. Unlimited displacement between the twoassemblies16 and18 could result in an excessive compression force on thechest12 which could injure the patient.

An alternative to thearm assemblies16 and18 shown in FIG. 1 is thearm assemblies416 and418 shown in FIG.13. Thearm assemblies416 and418 are made up of the spaced,parallel arms422,424,426 and428, respectively. The curved shape of the arms422-428 making up thearm assemblies416 and418 has been found to be more advantageous than the angled shape of the arms making up thearm assemblies16 and18 shown in FIG.1. The advantage is found primarily in the means for limiting the relative displacement of thearm assemblies416 and418. The preferred means for limiting the relative displacement is shown in greater detail in FIG.14.

As thearms422 and426, shown in FIG. 14, pivot about the common fulcrum located at thepivot pin430, they pivot toward thestop pin432. Thestop pin432 extends through one of three holes formed in an upright434 which extends rigidly from thebase414. Thearm422 has threeshoulders440,442, and444 which face thestop pin432. Thearm426 has threesimilar shoulders446,448 and450. In their relaxed position shown in FIG. 14, thearms422 and426 have gaps of a predetermined distance between corresponding shoulders. For example, the gap betweenshoulder442 andshoulder448 is a predetermined size when thearms422 and426 are in their relaxed position. As thearms422 and426 are pivoted toward one another, the gaps between the shoulders decrease in size. In order to insure that the gap between a particular pair of shoulders does not decrease below a specified minimum, thestop pin432 is placed in one of the threeholes452,454 or456 formed in theupright434. Each hole has an axis which extends into a particular gap. Since the three gaps between the six shoulders440-450 are of different length, the position of thestop pin432 in the upright434 will affect the distance thearms422 and426 can travel until two associated shoulders seat against thestop pin432, restricting further displacement.

For example, FIG. 15 shows thearm assemblies416 and418 in their relaxed positions and in phantom in an extended position. In the extended position, when thestop pin432 is positioned in thehole456 of the upright434, theshoulders440 and446 seat against thestop pin432 to limit the extension of thearm assemblies416 and418.

Thebelt40, which extends around the front, sides and back of the chest, is substantially inelastic and flexible. A plurality ofindicia50 is imprinted on the exposed surface of thebelt50. Thebelt40 attaches to thestrut34 on one side of thechest12, and extends around a major portion of the circumference of thechest12 to attach to the other strut36. When theassemblies16 and18 pivot around thepivot pin20, thebelt40 is tightened by thestruts34 and36 to which thebelt40 attaches.

Although thebelt40 is described as extending around the front, sides and back of the chest, the belt may be made up of two or more component parts, such as a pair of belts. This pair of belts could extend from attachment to thestruts34 and36, extending downwardly past the sides of the patient's chest to rigid attachment to a board which spans the width of the back of the chest. Therefore, “a belt wrapped around the chest” can be made up of two or more belt components which extend around portions of the chest circumference in combination with other rigid or flexible components.

The relaxed and mid-actuated positions of the arms of theapparatus10 are shown in FIG.2. The first andsecond assemblies16 and18 are shown in their relaxed position and (in phantom) at the mid-point of their actuated position. Theassemblies16 and18 are biased into the relaxed position by a spring (not shown) which could be a torsion spring extending aroundpin20 and connecting to theassemblies16 and18. The handle ends80 and82 of thearms22 and26 pivot along an arcuate path downwardly and away from each other, and the belt ends84 and86 of thearms22 and26 pivot upwardly and toward one another in an arcuate path subtending the same angle as the handle ends80 and82. Thebelt extremities88 and90 (which are the looped ends of thebelt40 which attach to thestruts34 and36) follow the belt ends84 and86 of the arms to an upward and more proximally spaced position. Since thebelt40 is substantially inelastic, its circumference will decrease under the force applied to it by thestruts34 and36, thereby tightening thebelt40 around thechest12.

Thebelt40 extends throughslots44 formed in a backboard42 which, when in use, is positioned beneath thechest12 of the patient. Thebelt40 preferably seats against a slidingmechanism43 which permits sliding of thebelt40 along the length of thechest12 for positioning of thebelt40 on thechest12. The backboard42 is made of a strong, lightweight material such as plastic and is wide enough to span the width of the chests of a large majority of the population. The backboard42 has a padded, raisedportion46 which elevates the patient's neck above his head for opening the breathing passages, and the backboard42 preferably hashandles250 and252 (shown in FIG. 9) for carrying the backboard42 with or without a patient lying on it. The backboard42, the attachedbelt40 and theassemblies16 and18, are all hung on a wall by extending hooks through thehandles250 and252 or by some other conventional hanging means, and may be hinged near the center for folding during storage.

Anoxygen tank100 and amask102 are shown in hidden lines in FIG. 2 as contained within achamber104 formed in thebackboard42. Agauge103, indicating the amount of oxygen in thetank100, is visible through theport101. The raisedportion46 of the backboard42 is suited to the formation of acylindrical chamber104 in which theoxygen tank100 can be easily stored. If needed, themask102 can be withdrawn from thechamber104 and placed over the patient's mouth for enhanced ventilation of the patient's lungs.

Theapparatus10 is operated in the following manner, referring to FIGS. 1 and 2. The victim is placed onto the backboard42 with his or herchest12 in the position shown in FIG.1. The back of the patient'schest12 seats against the surface of the backboard42 with the patient's neck resting on the raisedportion46 and his head lying on the horizontal surface on which the backboard42 lies, such as a floor. Thebase14 of theapparatus10 is placed at approximately the center of the patient'schest12 near the sternum. Thebelt40 is then extended upwardly from the backboard42, between the arms andchest12, and around opposite sides of thechest12 to match the relaxed contour of thechest12. Thebelt40 is positioned as high on thechest12 and as high under the underarms as possible.

Thebelt40 is next extended around thestruts34 and36, passing first between eachstrut34 and36 and thebase14. Thebase14 is more exactly positioned near the center of thechest12 by matching theindicia50 on thebelt40 on opposite sides of thebase14. Theindicia50 are alphanumeric characters spaced equally along the length of thebelt40 in a preferably identical arrangement at both ends of thebelt40. The indicia could, of course, be colored bands or other symbols.

Once thebelt40 extends around thestruts34 and36, the ends of thebelt40 are folded back over onto the portion of thebelt40 contacting thechest12 and are attached thereto by fasteners. Before fastening, though, theindicia50 at bothstruts34 and36 must match. For example, the number “3” is shown as the highest number on thebelt40 visible in FIG.1. In this example, the same number (“3”) should be the highest number visible at bothstruts34 and36, which indicates that an equal length of thebelt40 extends from the backboard42 to thestrut34 as to the strut36, and therefore that thebase14 is centered on thechest12.

After fastening thebelt40 to thestruts34 and36, the stroke limiter pins60 and62 extend into theholes1 and4 in thearms26 and28. Since the number “3” is the highest visible number on thebelt40, the limiter pins60 and62 are placed in the distal of the six holes1-6 inarms26 and28. If the number “2” were the highest number visible on thebelt40, the center holes2 and5 of the six holes1-6 on thepivot arms26 and28 would be used, since the number “2” would indicate a larger chest circumference than when “3” is the highest visible number. The stroke when the number “2” is the highest visible number is greater than when “3” is the highest visible number. This means for a larger chest circumference, the apparatus would be permitted to cause greater displacement of thechest12.

If thearm assemblies416 and418 shown in FIG. 13 are used rather than thearm assemblies16 and18 shown in FIG. 1, then the highest number visible on thebelt40 would indicate the positioning of thestop pin432 in theupright434. For example, since the number3 is the highest number visible on thebelt40 in FIG. 1, thestop pin432 would be placed in thehole456 which has the indicium “3” next to it. The indicium “3” is visible in FIG. 15, but only the indicia “1” and “2” can be seen in FIGS. 13 and 14.

Once theapparatus10 is positioned with thebelt40 around thechest12, thebase14 is centered and thelimiters52 and54 are in the correct position for thevisible indicia50 on thebelt40, the rescuer depresses theswitch70. This causes thelights72 to begin emitting a periodic, visible signal and the base14 to emit a periodic, audible signal in synchronization with thelights72. The rescuer then grips handles30 and32 with his or her hands and, with a downwardly directed force toward thechest12, pushes thehandles30 and32, pivoting them about thepivot pin20, thereby pivoting thearms22,24,26 and28 through arcuate paths about thepin20. This pivoting motion causes thestruts34 and36 at the opposite ends of the arms from thehandles30 and32 to pivot about thepivot pin20 in a direction away from thechest12, but with a smaller displacement than thehandles30 and32. Pivoting of thestruts34 and36 draws the ends of thebelt40 closer together, thereby tightening thebelt40 around thechest12. Since thebelt40 is inelastic, tightening of thebelt40 compresses thechest12. The arcuate motion of thehandles30 and32 is limited to a maximum displacement by thestroke limiters52 and54, when thepins60 and62 contact the ends of theslots64 and66. The force on thehandles30 and32 is released and then exerted again by the rescuer after thehandles30 and32 have returned to their original positions.

By cyclically depressing with a downwardly directed force, and releasing thehandles30 and32 (preferably in phase with the lights72), the rescuer cyclically tightens and loosens thebelt40 around the patient'schest12. The base14 concentrates some of the tightening force of the belt in thechest12 center and prevents pinching of the chest by the scissor-like assemblies16 and18. Thebelt40 tightening around thechest12 represents the “thoracic pump” method of artificially inducing blood flow in a cardiac arrest patient by applying a circumferential compressive force to a large area. The large force is from the leverage created by the scissor-like assemblies16 and18, and the large area is the circumference of thechest12.

As thefirst assembly16 and thesecond assembly18 are forced downwardly toward the chest, the base sole92 is forced downwardly along a path directed into, and preferably perpendicular to, the chest surface by the downwardly directed force on thehandles30 and32. Therefore, each depression of the first andsecond assemblies16 and18 results in a downward compression of the center of the chest by thebase14. This is the “cardiac pump” method of inducing blood flow by compressing the heart between the spine and the sternum.

Compressing the organs using the present invention takes advantage of both the “thoracic pump” (belt tightening and loosening) and “cardiac pump” (chest is depression by the base14) methods to convey blood through the blood vessels and, upon release, draw blood back into the organs. Upon each increase in pressure, the blood is compressed out of the organs (and air out of the lungs) and along the vascular system. Upon release, other blood is pulled in. Since the veins have a series of one-way valves, the periodic raising and lowering of thoracic pressure with the present invention creates an artificial blood flow supplying necessary elements to the vital organs, such as the brain, which increases the patient's chances of survival.

Thepivoting assemblies16 and18 comprise a force converter which converts the downwardly directed chest compressing force applied to thehandles30 and32 into multiple resultant forces. These resultant forces include a downwardly directed force applied from the base14 into thechest12 and two equal tangential forces applied by thestruts34 and36 to thebelt40. The forces are applied tangentially to thechest12 since thebelt40 wrapped around thechest12 and pulled taut must be tangential to thechest12 surface if it contacts the chest at the chest sides as shown in FIG.1. Theassemblies16 and18 comprise the force converter which is a device that converts the force manually applied to thehandles30 and32, and directed toward thechest12, into the resultants described above (specifically, a chest compressing resultant and a pair of belt tightening resultants).

A converter for converting the above described applied force into the resultants includes all equivalents to the preferred force converter. A converter need not merely redirect a specific force but could amplify, reduce or signal a device to generate other forces, by the application of a force.

The force necessary to generate sufficient pressure in the chest cavity to create blood flow can be generated by an average person if a device utilizes an applied force correctly. In the position in which a cardiac arrest patient is normally found, a rescuer cannot normally, without leverage, generate a downward force into the patient's chest sufficient to generate the necessary intrathoracic pressure without the risk of injury. The apparatus of the present invention uses the force which an average person can apply and converts the applied force into resultant forces in the directions needed while limiting the maximum displacement of the chest to prevent injury.

The force converter described above can be considered as a free body shown in FIG. 3 having an appliedforce112 directed downwardly onto theconverter110. Anopposite force114 is applied by the chest against theconverter110 as a reactbion to theopposite force112. Thetangential forces116 and118 are the forces of the belt, extending circumferentially around the chest, pulling on theconverter110. Theconverter110 converts the downwardly directedforce112 intoresultant forces120,122, and124. Theresultant force120 is directed into the chest along a direction similar to the appliedforce112. Theresultant forces122 and124 apply a tangential tension force to the belt which is tangential to the patient's chest.

The preferred embodiment of the present invention is one device the Applicants have found advantageous for converting thedownward force112 into the threeresultant forces120,122 and124. The Applicants know that many apparatuses are equivalent to, and could be substituted for, the preferred apparatus to provide the force conversion described in association with FIG.3. Although it is impossible to list every mechanical device which one skilled in the art will know can convert an applied force into the desired resultant forces, some of the many equivalents are described herein. However, this is not an exhaustive list, and other equivalents exist as will become apparent to those skilled in the art.

FIG. 4 shows a diagrammatic illustration of acam140 and a pair ofcam followers142 and144. Upon the application of a downward force by thecam140 onto a pair ofinclined surfaces143 and145, thefollower142 will slide rightwardly and thefollower144 will slide leftwardly, thereby exerting forces on the belt ends attached thereto, tightening the belt. Thecam140 will slide down the inclined surfaces offollowers142 and144, and upon reaching thehorizontal surfaces146 and148, will stop abruptly—exerting a downward force onto the surface beneath thefollowers142 and144, which could be the base of the present invention. The apparatus of FIG. 4 is equivalent to the preferred force converter apparatus.

FIG. 5 shows a diagrammatic illustration of a first eccentric150 and a second eccentric152 pivotally mounted to abase154. Amanual actuator156 attaches to a second pivot on each eccentric. A pair of belt ends158 and160 wrap around theeccentrics150 and152, respectively. Upon the application of a downwardly directed force on theactuator156, theeccentrics150 and152 pivot about the pivot points, exerting a force on the belt ends158 and160 causing a tightening of the belt. Theeccentrics150 and152 will, upon a sufficient downwardly directed force on theactuator156, impact upon thebase154, exerting a downwardly directed force on the base154 as in the preferred embodiment. The apparatus of FIG. 5 is equivalent to the preferred embodiment.

FIG. 6 illustrates a diagrammatic illustration of another equivalent to the preferred embodiment including anactuator170 to which a downwardly directed force is applied. Theactuator170 has a two-sidedtoothed surface172 which inter-engages with a pair ofgears174 and176.Gears174 and176 are pivotally mounted to abase178 and a pair of belt ends180 and182 wrap around a pair ofdrums184 and186 at each of thegears174 and176. Thetoothed surface172, upon a downwardly applied force to theactuator170, causes the inter-engaging gears174 and176 to rotate, thereby applying a force to theends180 and182 of the belt. The actuator170 impacts the base178 upon being actuated to a certain extremity, thereby exerting a downwardly directed force to the base178 as in the preferred embodiment.

Another alternative,mechanical apparatus260 which is equivalent to the preferred embodiment is shown in FIG.11. Theapparatus260 has a pair of pivotingarms262 and264 which pivot about apivot axis266 on abase268. Abelt270 attaches at opposite longitudinal ends to thearms262 and264. Thebase268 is positioned on a patient'schest272, thebelt270 is extended circumferentially around thechest272 and attached to thehandles262 and264. A downwardly directed force is applied to thehandles262 and264, tightening thebelt270 as thearms262 and264 pivot about thepivot pin266. In addition to the tightening of thebelt270, thebase268 is forced downwardly into thechest272.

FIG. 12 shows a two-chamber device having a base300 and two pivotingarms302 and304. Twosprings306 and308 keep twoarms302 and304 biased upwardly within thechamber310. Aplunger312 is biased away from thechamber310 by aspring314. Thebelt316 is attached to thearms302 and304. Upon downward compression of theplunger312, thearms302 and304 are rotated counterclockwise and clockwise, respectively. This rotation tightens thebelt316 and a patient's chest is compressed with the tightenedbelt316 and with thebase300, especially when theplunger312 reaches the lower limit of thechamber310.

Many illustrations show equivalent substitute devices for converting an applied force into the desired resultant forces. Most of those described above show purely mechanical equivalents to the preferred embodiment. As a person skilled in the mechanical arts will quickly find, there are many other different substitutes for the preferred embodiment. These devices are equivalent to the preferred embodiment or one of the alternatives described above and shown in the drawings. In addition to purely mechanical alternatives to the preferred embodiment, it is of course possible to combine mechanical, electrical, hydraulic and many other elements to arrive at an equivalent substitute for the preferred embodiment. These combination equivalents are discussed below.

In FIG. 7 a mechanical and electrical combination equivalent is shown diagrammatically including anactuator200 and anelectric motor202 attached to abase204. Themotor202 has a pair of belt ends206 and208 attached to adriveshaft210. Upon depression of theactuator200, a pressure-sensitive switch212 actuates themotor202, rotating thedriveshaft210 and exerting a linear force on the belt ends206 and208. As the force is applied to theactuator200, this downwardly directed force is transmitted through the base204 to the patient's chest which lies directly beneath thebase204. The embodiment of FIG. 7 is equivalent to the preferred embodiment.

FIG. 8 shows still another equivalent to the present invention in a diagrammatic illustration including ahydraulic cylinder220,fluid lines222 and224, andpistons226 and228 slidingly mounted within thecylinder220. The belt ends230 and232 are mounted to thepistons226 and228. Upon actuation of anactuator234, hydraulic fluid is forced into thehydraulic cylinder220 forcing thepistons226 and228 toward one another longitudinally, thereby exerting a force on the belt ends230 and232. The actuation of theactuator234 is accomplished by a downwardly directed force which exerts a similar force to a patient's chest lying directly beneath thehydraulic cylinder220.

Theactuator234 could be attached to a central piston which compresses a fluid within a hydraulic cylinder. Upon actuation ofactuator234, the hydraulic fluid within the cylinder is compressed and is conveyed through thelines222 and224 and thepistons226 and228 are driven inwardly as described above. This embodiment is also equivalent to the preferred embodiment.

It is possible to attach a power unit, such as a prime mover, to theapparatus10 which could function as an actuator to apply a lateral force to thearm assemblies16 and18 to actuate them automatically and in regular, periodic intervals. As shown in FIG. 9, thepower unit254 has acable256 which attaches to abelt258. The device providing a mechanical force to thebelt258 may be located in thepower unit254 and thecable256 is then rotatingly driven or longitudinally, reciprocatingly driven to tighten and loosen thebelt258. Alternatively, the actuator which tightens and loosens thebelt258 could be located beneath thebelt258 and thecable256 would merely convey electrical power or fluid pressure to the actuator. Thepower unit254 may use computer controls to time the application of force.

An example of apower unit280 applying a force which tightens abelt282 and depresses abase284 is shown in the development of another person appearing in FIG.10. As therod286 extends inwardly and outwardly of thepower unit280, thebase284 is displaced upwardly and downwardly, depressing thechest288 as described with the preferred embodiment. Furthermore, this same mechanical motion of therod286 tightens and loosens thebelt282 as with the preferred embodiment.

In order to ensure that the patient's lungs are allowed to expand as much as desired, it may be necessary to include a full-release indicator with the present invention. This indicator should have some means for alerting the rescuer when full release of the tension on the belt has not occurred. This indicator may include a limit switch, a magnet reed relay or contacts on the base14 against which thearm assemblies16 and18 rest in their relaxed position.

Instead of an indicator of full release, a mechanism could be added to thearm assemblies16 and18 for preventing the application of force to thehandles30 and32 until full release (and return to the relaxed position) has occurred. A ratchet mechanism having discreet spacings could be used for this purpose. Additionally, such mechanisms are commonly found on electrical crimping tools for loose terminals.

It is possible to build into the force converter a mechanism for storing and suddenly releasing energy during the application of a downward force. The sudden release would be actuated during the withdrawal of the downward force, applying a short duration, high intensity force to the chest rather than a long duration application of force as with the preferred embodiment.

It is preferred that the apparatus which rests on the top of a patient's chest be as light in weight as possible. The reason for this is that after the patient's chest has been fully compressed, any weight which rests on top of the chest will tend to resist decompression of the chest once the compression force is removed. Reducing this weight minimizes the amount of unwanted compression during release and decompression of the chest.

Theadhesive pad500 shown in FIG. 16 could contain an electrode which is electrically attached to a voltage generating device as is conventionally known. Theadhesive pad500 could be used in combination with one ormore electrodes504 interposed along the length of thebelt506 or embedded in thebackboard508. These electrodes are used in the conventional manner to induce a current through thechest510 which is used for defibrillating the patient's heart. Any combination of two or more electrodes can be used to induce a current to defibrillate the heart.

Theelectrodes504 can be interposed at multiple positions along the length of thebelt506 or in thebackboard508, but there will preferably be a minimum of one electrode on the base512 (such as theadhesive pad500 which functions as an electrode) in addition to at least oneother electrode504. The reason it is desirable to have an electrode at least on the base512 is that at the furthest extent of compression of thechest510, the distance between the anterior and posterior outer surfaces of thechest510 will be at a minimum, and the base512 will be positioned closer to the heart than at any other point in the whole compression/decompression cycle. At this point there is a minimum of resistance to the flow of current which gives the greatest current flow through the heart with the least likelihood of injuring the patient'schest510 tissue.

Theelectrodes504 can be positioned not only circumferentially about thechest510, but can also be positioned at the same circumferential location but at various longitudinal spacings.

It is preferred that a means be adapted to limit the travel of theassemblies416 and418 shown in FIG. 13 to only permit theassemblies416 and418 to move equal amounts relative to the base. It is undesirable for one assembly to move to one side more than the other assembly, since this causes an imbalance in the application of force, which may result in injury to the patient. The injury arises when a greater force is applied to one edge of the base than the opposite. This can occur if one of the twoassemblies416 and418 moves a substantially greater distance than the other assembly. One means for limiting their relative motion is a pin in aligned slots in the arms. Another is a gear mechanism connected to bothassemblies416 and418.

While certain preferred embodiments of the present invention have been disclosed in detail, it is to be understood that various modifications may be adopted without departing from the spirit of the invention or scope of the following claims.

Claims (68)

What is claimed is:

1. A CPR apparatus for increasing the flow of blood in a patient, said apparatus comprising:

(a) a base contoured to seat near a central region of said patient's chest;

(b) a manual actuator;

(c) a substantially inelastic belt means having first and second sections for wrapping around said chest; and

(d) a force converter mounted on said base, connected to said actuator and having belt connectors for connecting to said first and second sections of said belt means, for converting a force manually applied to said actuator and directed inwardly toward said chest into (1) a chest compressing resultant directed through said base toward said chest and (2) belt tightening resultants applied to said belt connectors directed tangential to said chest whereby the inwardly and tangentially directed force increases the blood flow in the natural direction.

2. The apparatus of claim1 wherein said manual actuator comprises first and second hand grippable handles.

3. The apparatus of claim2 wherein said converter comprises:

(a) a first arm having a first handle end to which said first handle is mounted and having an opposite, first belt end to which said first section of said belt means is attached, said first arm being pivotally mounted to said base at a first arm fulcrum generally intermediate said first handle and said first belt end; and

(b) a second arm having a second handle end to which said second handle is mounted and having an opposite, second belt end to which said second section of said of said belt means is attached, said second arm being pivotally mounted to said base at a second arm fulcrum generally intermediate said second handle and said second belt end.

4. The apparatus of claim2 wherein said converter comprises:

(a) a first assembly having a first pair of spaced, parallel first arms rigidly connected at first handle ends by said first handle, said first arms rigidly connected at opposite, first belt ends by a first strut, and said first arms pivotally mounted to said base at a first assembly fulcrum generally intermediate said first handle and first belt ends; and

(b) a second assembly having a second pair of spaced, parallel second arms rigidly connected at second handle ends by said second handle, said second arms rigidly connected at opposite, second belt ends by a second strut, and said second arms pivotally mounted to said base at a second assembly fulcrum generally intermediate said second handle and second belt ends.

5. The apparatus of claim4 wherein one of said first arms of said first assembly pair and one of said second arms of said second assembly pair are mounted to a side of said base, and the other arm of said first assembly pair and the other arm of said second assembly pair are mounted to an opposite side of said base.

6. The apparatus of claim5 wherein said assembly fulcrums coincide at a pivot pin extending through all said arms of said assemblies and through said base.

7. The apparatus of claim6 wherein said belt ends have longitudinal axes between said belt ends and said assembly fulcrums and said handle ends of said arms have longitudinal axes between said handle ends and said assembly fulcrums, and the belt end axis of each arm is nonparallel to the handle end axis of the same arm.

8. The apparatus of claim7 wherein an angle of about 120° is formed between said belt end axis of each arm and said handle end axis of the same arm.

9. The apparatus of claim6 wherein said arms are curved.

10. The apparatus of claim5 wherein a pair of stroke limiting bars is pivotally mounted to said pair of first arms of said first assembly, between said fulcrums and said first handle ends of each of said first arms, extending to sliding attachment with said second pair of second arms of said second assembly, each of said stroke limiting bars extending between arms mounted to the same end of said base for limiting the relative displacement of the attached arms.

11. The apparatus of claim10 wherein said stroke limiting bars are adjustably, slidably attached to said second pair of second arms of said second assembly, for adjusting stroke limitation.

12. The apparatus of claim5 further comprising at least one pair of facing shoulders formed on a pair of opposing arms, one shoulder formed on each arm, to form a gap between the facing shoulders into which a stop pin extends, for limiting the relative displacement of the opposing arms.

13. The apparatus of claim5 further comprising:

(a) three shoulders formed on each of two opposing arms, forming three gaps of different length between three pairs of facing shoulders;

(b) an upright mounted to said base and having three holes formed through said upright, each hole corresponding to one gap; and

(c) a stop pin extending from insertion in one of said holes into one of said gaps, for adjustably limiting the relative displacement of the opposing arms.

14. The apparatus of claim4 wherein said first belt section is conformed to attach to said belt end of at least one arm of each assembly and said second belt section is conformed to attach to said belt end of at least one arm of each assembly.

15. The apparatus of claim4 wherein said first belt extremity is conformed to attach to said first strut, said second belt extremity is conformed to attach to said second strut.

16. The apparatus of claim15 further comprising fasteners mounted to said first and second sections of said belt means.

17. The apparatus of claim16 wherein said fasteners comprise hooks and loops material.

18. The apparatus of claim16 further comprising indicia imprinted on a surface of said belt means corresponding to a length of each of said belt sections.

19. The apparatus of claim18 wherein belt means comprises a belt and said indicia are colored bands oriented transverse to a longitudinal axis of said belt.

20. The apparatus of claim4 further comprising a rigid, substantially planar backboard to which said belt means is attached.

21. The apparatus of claim20 wherein said backboard has two spaced, parallel slots through which said belt means extends.

22. The apparatus of claim21 wherein said backboard has a raised portion, integral with a planar portion, conformed to receive and support said patient's neck above said planar portion.

23. The apparatus of claim22 further comprising a pressurized gas container, hose and breathing mask housed within said backboard, beneath said raised portion.

24. The apparatus of claim23 further comprising a force sensor coupled to said base, and a force indicator coupled to said sensor and to said base.

25. The apparatus of claim24 further comprising a signal generator, coupled to said base, for producing periodic signals.

26. The apparatus of claim4 further comprising a means mounted on a chest-contacting surface of said base for adhering said chest-contacting surface of said base to said chest.

27. The apparatus of claim26 wherein said means for adhering comprises a suction cup.

28. The apparatus of claim26 wherein said means for adhering comprises an adhesive.

29. The apparatus of claim1 further comprising a pair of spaced electrodes mounted to said apparatus for contacting two spaced outer chest surfaces.

30. The apparatus of claim29 wherein a first electrode is mounted to a base outer, chest-contacting surface, and a second electrode is mounted to an apparatus chest-contacting surface which is spaced from said first electrode.

31. The apparatus of claim30 wherein said second electrode is mounted to said belt means.

32. The apparatus of claim31 further comprising a plurality of electrodes interposed along a longitudinal axis of said belt means.

33. The apparatus of claim1 further including means, coupled to said converter for limiting the magnitude of the belt tightening resultants from a force manually applied to said force converter.

34. The apparatus of claim33 wherein said means for limiting the magnitude of said belt tightening resultants limits said magnitude to a preselected one of a plurality of magnitudes.

35. The apparatus of claim34 further comprising indicia imprinted on a surface of said belt means corresponding to a length of each belt extremity.

36. The apparatus of claim35 further comprising indicia coupled to said limiting means corresponding to said preselected magnitude.

37. The apparatus of claim36 wherein said indicia coupled to said limiting means, is keyed to said indicia imprinted on said surface of said belt means.

38. The apparatus of claim37 wherein said manual actuator comprises first and second hand grippable handles and wherein said converter comprises:

(a) a first assembly having a first pair of spaced, parallel first arms rigidly connected at first handle ends by said first handle, said first arms rigidly connected at opposite, first belt ends by a first strut, and said first arms pivotally mounted to said base at a first assembly fulcrum generally intermediate said first handle and first belt ends; and

(b) a second assembly having a second pair of spaced, parallel second arms rigidly connected at second handle ends by said second handle, said second arms rigidly connected at opposite, second belt ends by a second strut, and said second arms pivotally mounted to said base at a second assembly fulcrum generally intermediate said second handle and second belt ends.

39. The apparatus of claim38 wherein a pair of stroke limiting bars is pivotally mounted to said pair of first arms of said first assembly, between said fulcrums and said first handle ends of each of said first arms, extending to sliding attachment with said second pair of second arms of said second assembly, each of said stroke limiting bars extending between arms mounted to the same end of said base for limiting the relative displacement of said attached arms.

40. The apparatus of claim39 wherein said stroke limiting bars are adjustably, slidably attached to said second pair of second arms of said second assembly, for adjusting stroke limitation.

41. The apparatus of claim38 further comprising at least one pair of facing shoulders formed on a pair of opposing arms, one shoulder formed on each arm, to form a gap between said facing shoulders into which a stop pin extends, for limiting the relative displacement of said opposing arms.

42. The apparatus of claim38 further comprising:

(a) three shoulders formed on each of two opposing arms, forming three gaps of different length between three pairs of facing shoulders;

(b) an upright mounted to said base and having three holes formed through said upright, each hole corresponding to one gap; and

(c) a stop pin extending from insertion in one of said holes into one of said gaps, for adjustably limiting the relative displacement of said opposing arms.

43. The apparatus of claim1 further comprising a force sensor coupled to said base, and a force indicator coupled to said sensor and to said base.

44. The apparatus of claim43 further comprising a signal generator, coupled to said base, for producing periodic signals.

45. A method of CPR treating a patient comprising:

(a) seating a base of a blood flow increasing apparatus on said patient's chest near a central region of said chest;

(b) wrapping a belt means having first and second sections around said patient's chest;

(c) fastening to said apparatus any of said first and second sections not already fastened to said apparatus;

(d) applying a force, directed inwardly toward said chest, to a manual actuator mounted to a converter, said converter connected to said base and said belt means; and

(e) converting said force into (1) a chest compressing resultant directed toward said chest and (2) belt tightening resultants directed tangentially to said chest whereby the inwardly and tangentially directed force increases the blood flow in the natural direction.

46. The method of claim45 wherein applying said force further comprises grasping a pair of hand grippable handles and applying a force having a component directed toward said chest.

47. The method of claim45 further including limiting the application of said force to one of a plurality of preselected limits.

48. The method of claim47 further including observing the length of said belt means required to wrap around said patient's chest and limiting said application of said force to the one of a plurality of preselected limits dependent upon the observed length of said belt means.

49. The method of claim45 further including periodically repeating the application of said force.

50. The method of claim45 further including periodically producing a signal and applying said force in response to said produced signal.

51. A CPR apparatus for increasing the flow of blood in a patient, the apparatus comprising:

(a) a base configured to seat near a central region of said patient's chest;

(b) an actuator;

(c) a substantially inelastic belt means having first and second sections configured to wrap around said chest; and

(d) a force converter mounted on said base, connected to said actuator and having belt connectors for connecting to said first and sections of said belt means, for converting a force applied by said actuator into (1) a chest compressing resultant directed inwardly toward said chest and (2) belt tightening resultants directed tangentially to said chest whereby the inwardly and tangentially directed force increases the blood flow in the natural direction.

52. The apparatus of claim51 wherein said actuator comprises a prime mover.

53. The apparatus of claim52 wherein said force converter comprises:

(a) a first arm having a first handle end and an opposite, first belt end to which said first section of said belt means is attached, said first arm being pivotally mounted to said base at a first arm fulcrum generally intermediate said first handle and said first belt end; and

(b) a second arm having a second handle end to which said second handle is mounted and having an opposite, second belt extremity to which said second section of said belt means is attached, said second arm pivotally mounted to said base at a second arm fulcrum generally intermediate said second handle and said second belt end.

54. The apparatus of claim52 wherein said force converter comprises:

(a) a first assembly having a first pair of spaced, parallel first arms rigidly connected at first handle ends by said first handle, said first arms rigidly connected at opposite, belt ends by a first strut, and said first arms pivotally mounted to said base at a first assembly fulcrum generally intermediate said first handle and first belt ends; and

(b) a second assembly having a second pair of spaced, parallel second arms rigidly connected at second handle ends by said second handle, said second arms rigidly connected at opposite, second belt ends by a second strut, and said second arms pivotally mounted to said base at a second assembly fulcrum generally intermediate said second handle and second belt ends.

55. The apparatus of claim54 wherein one of said first arms of said first assembly pair and one of said second arms of said second assembly pair are mounted to a side of said base, and the other first arm of said first assembly pair and the other second arm of said second assembly pair are mounted to an opposite side of said base.

56. The apparatus of claim55 wherein said assembly fulcrums coincide at a pivot pin extending through all said arms of said assemblies and through said base.

57. The apparatus of claim51 further including means, coupled to said converter for limiting the magnitude of the belt tightening resultants from a force manually applied to said force converter.

58. The apparatus of claim57 wherein said means for limiting said magnitude or said belt tightening resultants limits said magnitude to a preselected one of a plurality of magnitudes.

59. The apparatus of claim58 further comprising indicia imprinted on a surface of said belt means corresponding to a length of at least one of said first and second sections.

60. The apparatus of claim59 further comprising indicia coupled to said limiting means corresponding to said preselected magnitude.

61. The apparatus of claim60 wherein said indicia coupled to said limiting means is keyed to said indicia imprinted on a surface of said belt means.

62. The apparatus of claim60 wherein said force converter comprises:

(a) a first assembly having a first pair of spaced, parallel first arms rigidly connected at first handle ends by said first handle, said first arms rigidly connected at opposite, belt ends by a first strut, and said first arms pivotally mounted to said base at a first assembly fulcrum generally intermediate said first handle and first belt ends; and

(b) a second assembly having a second pair of spaced, parallel second arms rigidly connected at second handle ends by said second handle, said second arms rigidly connected at opposite, second belt ends by a second strut, and said second arms pivotally mounted to said base at a second assembly fulcrum generally intermediate said second handle and second belt ends.

63. The apparatus of claim62 wherein a pair of stroke limiting bars is pivotally mounted to said pair of first arms of said first assembly, between said fulcrums and said first handle ends of each of said first arms, extending to sliding attachment with said second pair of second arms of said second assembly, each of said stroke limiting bars extending between arms mounted to said same end of said base for limiting the relative displacement of said attached arms.

64. The apparatus of claim63 wherein said stroke limiting bars are adjustably, slidably attached to said second pair of second arms of said second assembly, for adjusting stroke limitation.

65. The apparatus of claim62 further comprising at least one pair of facing shoulders formed on a pair of opposing arms, one shoulder formed on each arm, to form a gap between the facing shoulders into which a stop pin extends, for limiting the relative displacement of said opposing arms.

66. The apparatus of claim62 further comprising:

(a) three shoulders formed on each of two opposing arms, forming three gaps of different length between three pairs of facing shoulders;

(b) an upright mounted to said base and having three holes formed through said upright, each hole corresponding to one gap; and

(c) a stop pin extending from insertion in one of said holes into one of said gaps, for adjustably limiting the relative displacement of said opposing arms.

67. The apparatus of claim51 further comprising a force sensor coupled to said base, and a force indicator coupled to said sensor and to said base.

68. The apparatus of claim67 further comprising a signal generator, coupled to said base, for producing periodic signals.

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